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Paleoekologia i paleośrodowisko późnego kampanu na podstawie wybranych profili z doliny środkowej Wisły

100%

Zatoń M.

tom Vol. 51, nr 8

678-684

Trzy odsłonięcia górnego kampanu, należące do trzech kolejnych poziomów amonitowych (Neancyloceras phaleratum, Bostrychoceras polyplocum i Didymoceras donezianum) w dolinie środkowej Wisły, zostały zbadane pod kątem paleośrodowiskowym. Bogata makrofauna ze wszystkich szczebli troficznych, świadczy o spokojnym środowisku, odpowiadającemu dzisiejszej strefie pogranicza wewnętrznego i zewnętrznego szelfu, o normalnym zasoleniu, dobrze natlenionych wodach przydennych i podłożu o zróżnicowanej konsystencji, stwarzającego różnorodnej faunie odmienne nisze ekologiczne.

The paleoecology of macrofauna from three Upper Campanian outcrops in the Middle Vistula valley, belonging to three successive ammonite zones (Neancyloceras phaleratum, Bostrychoceras polyplocum and Didymoceras donezianum), have been investigated on paleoenvironmental ground. The rich macrofauna of all trophic levels indicates the calm epicratonic basin, corresponding to the inner to outer shelf environment, of normal salinity waters, good bottom-water oxygenation and with substrate of varied consistency, providing different niches for diverse fauna.

Konzentrat-Lagerstätte-type carbonate concretions from the uppermost Bajocian (Middle Jurassic) of the Częstochowa area, South-Cental Poland

63%

Zatoń M. , Marynowski L.

tom Vol. 48, No 4

339--350

Early-diagenetic calcitic concretions of latest Bajocian (parkinsoni Zone, bomfordi Subzone) age in the Polish Jura contain an extremely rich and well-preserved macrofauna. In addition to bivalves and brachiopods, there are numerous ammonites of the (sub)genera Parkinsonia, Nannolytoceras, Lissoceras (Lissoceras), L. (Microlissoceras), as well as rare representatives of Vermisphinctes, Strigoceras (Strigoceras) and Phylloceras. Carapaces of primitive prosopid crabs are found associated. Such a diverse and well-preserved fauna (previously unknown from Bajocian epicratonic deposits of the Polish Jura), is typical of Konzentrat-Lagerstätte-type deposits. The random distribution of the concretions in exposure and the small size of the fauna may suggest that all remains were concentrated by bottom-current action in small depressions on an uneven sea-floor. The presence of numerous small-sized ammonites may be regarded as reflecting post-spawning assemblages which sufferedmass-mortality. Although cause of their death remains unclear, storm events are a possibility. Such depressions acted as natural “traps” as well as constituted a size-limiting factor for the accumulating fauna. The fact that all elements are well preserved indicates brief post-mortem transport and rapid burial, followed by early diagenesis that protected them from compaction. The absence of such fossil-rich concretions higher in the Middle Jurassic sequence clearly shows that our current assessment of biotic diversity may be an underestimate. The carbonate concretions contain a predominantly terrestrial type of organic matter (OM). Samples analysed are extremely immature, but early diagenetic transformations of OM occurred prior to concretion formation.